Wash and chop rhubarb into small slices and place in fermentation vessel or a large bowl or pot.
Cover with sugar and stir to coat and evenly distribute. Cover with a lid or tea towel secured with a rubber band and let sit for 2-3 days. The sugar will extract juice from the rhubarb. (See notes below for an alternative method if you have a steam juicer.)
After 2-3 days you should have a lot of juice. Separate juice from rhubarb chunks. If the juice is not already in the fermentation vessel, put in there. Lightly rinse rhubarb chunks and save the rinse water. Add the rinse water to the fermentation vessel. If needed, add water until you have about a gallon of liquid in the vessel.
Add tannin and yeast nutrient and stir until dissolved.
Sprinkle about half the packet of yeast on top. If desired, you could bloom the yeast in a small amount of water first.
Cover with a lid with an airlock and let sit at room temperature for about six weeks to ferment. Every two weeks or so, rack the wine (transfer the wine) to a new fermentation vessel to remove it from the sediment.
When fermentation has fully stopped (and it may take longer than six weeks), siphon the wine into wine bottles, cork, and store. Rhubarb wine can be enjoyed immediately, but flavour does improve with aging.